He wasn’t recording anything like that.
The terrorist act in that Russian airport where the perp brought in a suitcase explosive and lit it in a group of people before his luggage was checked by security, could easily happen in the US.
It probably will happen while the TSA agents are strip searching an American baby’s diaper and arguing with the mom over her bottle of formula, sticking their hands in a four year old’s underwear or grabbing an granny’s croch and breasts because her pace maker set off the metal detector. The terrorist who arranges the bombing will have probably traveled, unobstructed, over the Mexican border with his explosives/nukes.
The man you saw could have been casing to see where his pals should lite up the suitcase for maximum slaughter Regardless, people are permitted to take photographs in terminals and TSA was too busy with the tasks listed above rather than performing security, to bother to check out why the man you reported was taking pictures.
The other issue is this. Had TSA not been molesting innocent Americans in a senseless security system designed for political correctness, people would not have taken them to court over their sensitivity to people recording the abusive actions of agents. One stupid action on the part of the government leads to a multitude of stupid reactions. With terrorism, that is not comforting at all.